Recently, optical recording/reproducing devices capable of recording and reproducing optical information on optical storage media such as BD (Blu-ray) Disks include optical heads capable of correcting spherical aberrations which occur when an optical beam passes on a recording surface of each of the optical media. An example of such optical heads can be seen in a conventional technology disclosed in Patent Literature 1 (Japanese Patent Application Publication, Tokukai, No. 2003-45068; Publication date: Feb. 14, 2003).
In a spherical aberration correction technique using the above-described optical heads, a core of a characteristic configuration is that a cluster of relay lenses movable along an optical axis is provided. The following specifically explains driving of the cluster of relay lenses. The cluster of relay lenses is held by a lens holder. The lens holder is driven along a guide rail, in connection with rotational movement of a lead screw connected to a stepping motor.
An example of such a driving technology in the field of optics can be seen in a driving unit disclosed in Patent Literature 2 (Japanese Patent Application Publication, Tokukaihei, No. 4-69070; Publication date: Mar. 4, 1992).
Patent Literature 2 discloses an invention related to a driving unit provided with a piezoelectric element expandable and contractible in a driving direction of a lens barrel (an optical axis direction) and a driving direction-changing member connected to one end of the piezoelectric element. FIG. 10 is a diagram illustrating a configuration of the driving unit disclosed in Patent Literature 2. As shown in FIG. 10, the driving unit according to Patent Literature 2 is provided with a piezoelectric element 301, a rod-shaped driving direction-changing member 302, a lens barrel (driven body) 304, a lens 3011, an image pickup device 3012 such as a CCD, and a circuit substrate 3013, all of which are held inside a housing 306. The piezoelectric element 301 is connected to one end of the rod-shaped driving direction-changing member 302, and the lens barrel (driven body) 304 and the driving direction-changing member 302 are frictionally engaged. Further, the lens 3011 is mounted in the lens barrel 304, while the image pickup device 3012 is positioned below the lens barrel 304. The image pickup device 3012 is fixed to the circuit substrate 3013 by, for example, soldering. According to Patent Literature 2, because the driving direction-changing member 302 is frictionally engaged with the lens barrel 304 (driven body), a frictional force occurs between the driving direction-changing member 302 and the lens barrel 304 when the piezoelectric element 301 connected to the driving direction-changing member 302 expands or contracts itself in the optical axis direction. This frictional force drives the lens barrel 304 along the optical axis.
In the driving unit shown on FIG. 10, due to the expansion and contraction of the piezoelectric element 301 in directions of arrows, the driving direction-changing member 302 is driven in the direction of the optical axis. As a result, the lens barrel 304 frictionally engaged with the driving direction-changing member 302 is driven in the optical axis direction.
However, the above-described conventional technology raises the following problems.
In the case of the conventional technology disclosed in Patent Literature 1, it is difficult to achieve height reduction for the device while a high level of correcting ability is maintained for the cluster of relay lenses. The reason for this is that reducing the length of the lead screw for reduction of the height of the device also results in a decrease in a range in which the cluster of relay lenses corrects the spherical aberration. In other words, the height reduction of the optical head device is difficult in the case of the conventional technology where the correcting ability of the cluster of relay lenses is ultimately limited by the length of the lead screw.
Further, in the case of the conventional technology disclosed in Patent Literature 2, height reduction is difficult to achieve in a configuration where the expansion or contraction direction of the piezoelectric element 301 is identical with the driving direction of the lens barrel 304. Further, miniaturization can only be achieved by miniaturizing the driving unit composed of the piezoelectric element 301 and the driving direction-changing member 302. When the piezoelectric element 301 is miniaturized, a displacement amount and a thrust decrease. This decreases a driving speed. Further, when the driving direction-changing member 302 is miniaturized, a driving stroke decreases.